Illuminated pushbutton switches used in commercial and military aircraft, boats and other vehicles are fairly uniform in size across various commercial suppliers. The switches are usually a generally rectangular cuboid with a length of approximately 2.5 inches and an end face ranging from about 0.75×0.75 inches to 1.5×1.5 inches, including non-square configurations (e.g., 1.0×1.5 inches). These switches normally include a cap and a frame or body, collectively housing incandescent or light emitting diode (LED) illumination sources, optical filters, legend plates, snap action mechanical switches, connectors, driver circuits, and other components. Switch sizing is generally selected by the aircraft, boat or vehicle manufacturer based on compatability with existing designs, interoperability with on-board control systems, and space and/or weight considerations.
Normally the interface and drive logic for connecting illuminated pushbutton switches to control systems within the vehicle is external to the switch. A controller prompting illumination or responding to actuation of the switch is disposed somewhere in the vehicle, normally connected to multiple illuminated pushbutton switches. The interface provides circuits, for example, for stepping down the 14 or 28 volts (V) direct current (DC) voltage normally available in aircraft in order to implement voltage-controlled dimming.
Specialized applications involving illuminated pushbutton switches may require electronic interface and drive functions such that depressing the pushbutton switch initiates an action, a conditional action or a timed response. The functional operation can be initiated by receiving inputs from the switch or may be a signal received from a remote location. The interface logic signal or timing pulse results in a signal output that can then be used to energize the local illuminated switch or/or activate another unit such as an illuminated indicator or a remote interface within a different device. Such functionality may involve a plurality of illuminated pushbutton switches in differing locations all interfacing through the same interface or logic units, wherein a switch depressed at one location may be modified by the interface circuitry or driven by the local switch circuitry.
For example, within the realm of illuminated pushbutton switch usage, specialized applications are emerging requiring inclusion of latching, blinking or remote control functions to be included within the illuminated pushbutton switch housing. Such applications may require depressing the pushbutton switch to initiate a remote action request, activating switch functions from a remote location, energizing or blinking a local or remote display, and resetting the switch state automatically upon remote acknowledgement. Other applications may involve a plurality of illuminated pushbutton switches in differing locations, all controlling the same functions, wherein a switch depressed at one location must change the state of a switch or display at another location. Nearly all applications require the added safety feature of an automatic reset to a default state after loss of power.
Proposed designs may incorporate local latching and remote release functions through the use of internal electromagnetic holding coils, in some cases together with various electronic or electromechanical means to interrupt the holding coil current locally without remote intervention. Many of the proposed designs that rely upon an internal electromagnetic holding coil suffer from excessive power consumption, excessive heat, sensitivity to shock and physical jarring, electrical spikes, holding coil drop-out on low voltage, and low reliability. The internal holding coil also makes the resulting illuminated pushbutton switch substantially longer and heavier than standard models that do not incorporate a holding coil.
There is, therefore, a need in the art for improved implementation of interface and relay functions for pushbutton illuminated switches.